1. Field of the Invention
The invention relates to a method for generating pulse edges, assigned synchronously to the movement of a mechanical part, whereby a magnetic field is generated and at least two measuring signals for the magnetic field are detected, whereby the magnetic field is changed as a function of the movement of the mechanical part in such a way that the measuring signals are modulated phase-shifted to one another. In addition, the invention relates to a semiconductor chip into which a magnetic field sensor and a signal processing unit associated therewith are integrated, whereby the magnetic field sensor has at least one first sensor element and a second sensor element, which are offset to one another and/or arranged with their measuring axes transverse to one another.
2. Description of the Background Art
A process of this type in which the sensor is designed as a soft magnetic gear disposed rotatable around an axis of rotation is disclosed in U.S. Pat. No. 5,637,995. A semiconductor chip, into which a magnetic field sensor having two magnetoresistive sensor elements is integrated, is arranged at the outer circumference of the sensor. A permanent magnet, whose magnetic flux penetrates the sensor elements and the gear, is arranged at the back of the semiconductor chip facing away from the gear. The sensor elements are formed approximately rod-shaped and inclined 45° in directions opposite to one another with their long axes toward the magnetization direction of the permanent magnets in a plane running at right angles to the axis of rotation of the gear. When the teeth of the gear move past the arrangement having the sensor elements and the permanent magnet, the direction of the magnetic flux at the sensor elements changes. The measuring signals of the sensor elements have in each case an approximately wave-shaped course, whereby the measuring signal of the one sensor element has a maximum when the measuring signal of the other sensor element has a minimum. The measuring signals are supplied to a signal converter stage, which generates a pulse edge at an output terminal, when the measuring signals pass through their maximum or minimum. The pulse edges are said to occur whenever a tooth flank of the gear moves past the magnetic field sensor. The method has the disadvantage that the detection of the maximum or of the minimum is beset with inaccuracies. As a result, a time shift may occur between the occurrence of a pulse edge and the time at which a tooth flank goes past the magnetic field sensor.